Northern Ireland's First Minister won a standing ovation at the Belfast conference, but was heckled and booed by internal party critics who want to pull out of the power-sharing government with Sinn Fein.

The leader accused anti-Agreement Unionists of rushing into "public attacks and simplistic responses" in the wake of the party's defeat in the by-election in South Antrim two weeks ago. "We will be more successful if we are united with a more mature approach," he argued. "That is why I won't be walking away from the Executive just yet. A considered and calibrated approach if others do meet their commitments will be better.

"I hear loud calls for a change of policy. I'll give those who have been shouting a change of policy. Stop undermining the party. Stop undermining the leadership of the party. Stop undermining democratic decisions made by your party. Stop running to the media and badmouthing the Assembly team."

The Waterfront Hall conference was Mr Trimble's last attempt to see off his critics, among them Jeffrey Donaldson, the hardline MP for Lagan Valley. In a bid to shore up by Mr Trimble's position, Downing Street has renewed pressure on the IRA to open more of its arms dumps to independent inspectors.

Mr Trimble said that, just as the Democratic Unionists, SDLP and Sinn Fein kept their differences to themselves, so must the Ulster Unionists. "There is no Utopia out there. Politics is a rough business with limited choices," he told them. "Will we sleep any sounder in our beds if we are seen to ditch this agreement? Will there be decommissioning? Will the Union be guaranteed? No, no and no again."

Party security spokesman Ken Maginnis criticised Mr Donaldson's supporters, but was loudly heckled when he mockingly said "the overall death rate is down by 70 per cent, maybe you should review this David". He drew howls of indignation when he said that the five years of Mr Trimble's leadership should be compared to the previous five years of leadership under Jim Molyneaux. Lord Molyneaux is reported to have left the auditorium shortly afterwards.

Many delegates were angered by Mr Maginnis's remarks and another delegate from his constituency, Tom Fleming, spoke of two families in Garvagh who had lost loved ones and feared seeing the killers responsible walking the street following prison releases. Another, Tom Robinson from Larne, wondered "if the party actually had a bottom line?"

Despite the slick presentation by the organisers, the rumblings from the floor were sufficient to underline Mr Trimble's immediate difficulties. Mr Trimble knows that time is running out for his policies, with anti-Agreement opponents confident of ousting him at another special meeting of the Ulster Unionist Council in early November. Close aides acknowledge that his opponents within the party have seized the initiative and have struck at a crucial time, with both Dublin and London "off message" to his critical position.